This application claims the benefit of Japanese Application No. 2000-393114 filed in Japan on Dec. 25, 2000, the contents of which are, incorporated by this reference.
1. Field of the Invention
The present invention relates to an image forming system and an optical screen unit. More particularly, the present invention is concerned with an optical screen unit having a major surface on which an image is projected, and with an image forming system.
2. Description of the Related Art
In the past, various proposals have been made on an optical screen unit having a major surface on which an image is projected from an image projector.
As such an optical screen unit, for example, Japanese Unexamined Patent Application Publication No. 7-43835 describes a translucent projection screen having a plurality of screen sheets arranged into an image projection surface of the screen. The translucent projection screen includes holding means that holds at least one joint portion between screen sheets. At this time, the holding means restricts movement of the joint portion so that the joint portion will be immovable in a direction substantially orthogonal to the joint portion but movable in a direction substantially parallel thereto. Thus, the displacement of the joint portion is minimized.
Furthermore, the translucent projection screen includes tensioning means that tensions each screen sheet to move towards edges of the image projection surface and that is provided in an ineffective part of each screen sheet, that is, the perimeter of each screen sheet on which no image is projected. The inclusion of the tensioning means eliminates a warp or deflection.
In order to efficiently introduce projected light to an observer, the screen of the optical screen unit is designed in various forms. For example, the screen is realized by arranging numerous beads into a plane, shaping a Fresnel lens sheet, or using lenticular lens sheets. Generally, an optical member having a diffusing surface is adopted in combination with the screen designed in any of the forms in order to realize a wide angle of visibility.
By the way, in a multi-projector system having a plurality of image-projectors arranged, a plurality of partial images are projected from the plurality of image projectors in order to form one image on a screen. A streak between partial images is discernible by an observer who sees the screen while staying in front of the system but may be discerned by an observer who sees the screen while staying obliquely to the system. Nevertheless, the optical screen unit designed in any of the foregoing forms is helpful in alleviating the problem.
Assume that the image projectors arranged without any measures taken may project images on a optical screen that has a seam (joint line) between screen sheets like the one described in the Japanese Unexamined Application Publication No. 7-43835. In this case, the seam may be discerned as a streak in a displayed image. This deteriorates images quality.
Moreover, even in the aforesaid optical screen unit for example, when the screen is realized with lenticular lens sheets, the lenticular lens sheets oriented in two directions must be superposed on each other for the purpose of obtaining a two-dimensional effect. Furthermore, in order to sharply display an image formed on the lenticular lens sheets without blurring the image, the lenticular lens sheets must be brought into close-contact with the optical member having the diffusing surface.
There is therefore an increasing demand for the technology for bringing optical sheets such as the lenticular lens sheets into close contact with the optical member having the diffusing surface such as an optical plate without occurrence of a warp or deflection.
Accordingly, an object of the present invention is to provide an image forming system in which streaks stemming from joint lines will be indiscernible in an image projected on an optical sheet having joint lines.
Another object of the present invention is to provide an optical screen unit whose optical sheet can be brought into close contact with an optical plate thereof without impairment of the sharpness of an image formed on the optical sheet.
Briefly, according to the present invention, there is provided an image forming system consisting mainly of fan optical sheet and image projectors. The optical sheet has a plurality of sheet members joined with the margins of adjoining sheet members met as a joint line so as to have one or more joint lines. The image projectors each produce an image or a part of an image and project the image or part of an image to the optical sheet through a projection optical system. Herein, when the joint lines do not cross each other in the optical sheet, the number of image projectors is equal to or larger than the number of joint lines. When the joint lines cross each other at a node, the number of image projectors is equal to or larger than the number of nodes. The image projectors are positioned to cope with any of three cases described below. Namely, in the first case, only one node exists within a field in the optical sheet on which an image projector projects an image or part of an image. In the second case, no node exists but only one joint line exists. In the third case, no joint line exists. Moreover, in the first case, the optical axis of a projection optical system included in an image, projector meets the node so as to fit the normal on the major surface of the optical sheet. In the second case, the optical axis of a projection optical system included in an image projector intersects the joint line at a point, and is contained in a plane defined with the normal on the major surface of thee optical sheet at the point and with the point on the joint line.
Moreover, according to the present invention, there is provided an image forming system consisting mainly of and optical sheet and an image projector. The optical sheet has a unique portion whose optical property is unique. The image projector projects an image on the optical sheet through a projection optical system. The image projector is positioned so that a solid angle formed with rays propagating from the projection optical system to the unique portion will be minimized under a restriction on a predetermined positional relationship to the optical sheet.
Furthermore, according to the present invention, there is provided an optical screen unit that has an image projected on the major surface thereof. The optical screen unit consists mainly of an optical plate, one or more optical sheets, and a close contact means. The optical plate has rigidity. The one or more optical sheets are arranged over the major surface of the optical plate and have flexibility. The close contact means brings the major surface of the optical plate and the major surfaces of the optical sheets into close contact with one another.
The above and other objects, features, and advantages of the invention will be more clearly understood from the following description referring to the accompanying drawings.